.TH SIGAVG 1 "25 November 2002" "WFDB 10.3.0" "WFDB Applications Guide"
.SH NAME
sigavg \- calculate averages of annotated waveforms
.SH SYNOPSIS
\fBsigavg -r\fR \fIrecord\fR \fB-a\fR \fIannotator\fR [ \fIoptions\fR ... ]
.SH DESCRIPTION
.PP
A common problem in signal processing is to determine the shape of a
recurring waveform in the presence of noise.  If the waveform recurs
periodically (for example, once per second) the signal can be divided
into segments of an appropriate length (one second in this example), and
the segments can be averaged to reduce the amplitude of any noise that
is uncorrelated with the signal.  Typically, noise is reduced by a factor
of the square root of the number of segments included in the average.  For
physiologic signals, the waveforms of interest are usually not strictly
periodic, however.  \fBsigavg\fR averages such waveforms by defining segments
(averaging windows) relative to the locations of waveform annotations.
.PP
\fBsigavg\fR requires a WFDB \fIrecord\fR containing any number of signals to
be averaged, and an annotation file containing markers (fiducial points) that
define a fixed point in the averaging window for each waveform.  By default,
all QRS (beat) annotations for the specified \fIannotator\fR are included in
an average that begins 50 ms before the annotation and ends 50 ms after the
annotation.  The output is in text form, with times (in seconds, relative to
the annotations) of each sample in the first column, and averages for each
signal in the remaining columns.
.PP
\fIOptions\fR include:
.TP
\fB-d\fR \fIdt1 dt2\fR
Set the measurement window relative to QRS annotations.  Negative values
correspond to offsets that precede the annotations.  Defaults: \fIdt1\fR =
-0.05 seconds;  \fIdt2\fR = 0.05 seconds.
.TP
\fB-f\fR \fItime\fR
Begin at the specified \fItime\fR in \fIrecord\fR (default: the beginning of
\fIrecord\fR).
.TP
\fB-h\fR
Print a usage summary.
.TP
\fB-H\fR
Read multifrequency records in high resolution mode (default: use low
resolution mode).
.TP
\fB-p\fR \fItype\fR [ \fItype\fR ... ]
Include annotations of the specified \fItype\fRs only (default: include all QRS
annotations).
.TP
\fB-t\fR \fItime\fR
Process until the specified \fItime\fR in \fIrecord\fR (default: the end of
the record).
.TP
\fB-v\fR
Verbose mode: print column headings above measurements.
.TP
\fB-z\fR
Set the baseline to zero before averaging.
.SH ENVIRONMENT
.PP
It may be necessary to set and export the shell variable \fBWFDB\fR (see
\fBsetwfdb\fR(1)).
.SH SEE ALSO
\fBcalsig\fR(1), \fBsetwfdb\fR(1), \fBsigamp\fR(1)
.SH AUTHOR
George B. Moody (george@mit.edu)
.SH SOURCE
http://www.physionet.org/physiotools/wfdb/app/sigavg.c
